Study On Offshore Wind Turbine Blade Fatigue Behavior Based On Atmospheric Stability And Air-sea Exchange Action

Offshore field is an empty area which has few obstacles of marine environment, so it has rich wind resources and stable wind field. Therefore, China has developed the martime power projects in recent years which lead to the higher requirements of offshine wind turbines. The fatigue damage is the main damage style of offshore wind turbine. This thesis research the wind characteristics around offshore wind turbine deeply. Based on the offshore wind field which consider the atmospheric stability and air-sea exchange action, and the wind turbine dynamic load characteristics which consider the wind turbine blade rotating effect, the offshore wind turbine fatigue characteristic analysis can be systematic researched.The accurate description of offshore mean wind velocity profile and fluctuating wind velocity spectrum around the offshore wind turbine is key of fatigue characteristic analysis. As we know, the offshore mean wind velocity profile and fluctuating wind velocity spectrum is the important factor to describe the wind field characteristics. And the field observations is important way to gain the reliable data. This thesis study how the atmospheric stability and air-sea action affect the mean wind velocity profile based on the offshore normal and typhoon wind data. And the new offshore mean wind velocity profile is put forward through modifying the logarithmic law model. At the same time, in order to analyse the influence of various parameters of the new model, the parameter sensitivity analysis is necessary.As for the offshore turbine blades, this thesis study how the rotation of wind turbine affect the fluctuating wind velocity spectrum based on the frequency domain and propose the new auto spectrum and cross spectrum expression. According to the measured data, the appropriate fluctuating wind velocity spectrum and coherence function can be determined. At the same time, the influence of spectral parameters of the rotation Fourier spectrum model is described by the parameters sensitivity analysis.Based on the study on the the wind field around the wind turbine, it reveals the fatigue properties of wind turbines affected by atmospheric stability and air-sea exchange action.Firstly, based on the offshore mean wind velocity profile and the rotation Fourier spectrum model, the wind characteristic around wind turbine can be simulated by harmony superposition method. And then considering the vasopressin-momentum theory to determine the wind turbine wind input load, the load spectrum can be gain by the dynamic analysis of ABAQUS software. Finally, based on the rain-flow counting method, the fatigue life is calculated by fatigue performance S-N curves and linear damage accumulation method.